so the TG glowing would potentially indicate that the engine is operating inefficiently, with combustion taking place in the TG and not in the cylinders
Yes, I think that's certainly possible, but there may be something else going on too. The claim is that the "exhaust gas temperature" (EGT) entering the TG is ~241C. This is below a normal range of EGTs for small generators. Here is a screengrab from the video showing the various temp readings:
Note that none of them are labeled EGT, but one is labeled "manifold" and while it's hard to read, it says 244C and a few seconds after this shot it raises to 301C. Nothing is labeled or explained much, but what if the "manifold" sensor is this one on top of the cylinder head, or possibly just below the union?
It's no measuring the EGT, the actual exhaust gas, rather, it's measuring the temperature of the cylinder head or maybe the union connecting the cylinder head to the TG. If so, then 241C is a perfectly normal temperature for a cylinder head on an air-cooled generator:
That it pops up to 300C probably means its overheating and not running correctly. We've already established that the EGT for a generator can get up to 487C with 315C being the normal average. Now take another look at the temperatures. The two highest numbers here are 301c for the manifold and 362C for the "lower pipe".
These temperatures are with the TG glowing red hot. He's measuring the temperature of the exterior manifold or cylinder head and then measuring the temperature of the TG, but he's not measuring the temperature of the exhaust gases flowing into the TG.
We have an overheating generator producing hotter than normal exhaust gases that are then flowing into a thin walled Tg and heating it up to the temperature of that exhaust gas.
It might fit with his list too. If T1 below is the same as "lower pipe1" and T4 is the same as "manifold" then they go together similar to what we're seeing on the above temperature read outs:
The max temperature of 767C could be a transitory spike after a few minutes of the generator running really, really hot. Note also the claim of a minimum temperature of -86.3C on T3 at the same time T1 was spiking. If I understand it all, while the outer shell of the TG was reaching 767C, the inner section was outputting air(?) at -86C.
i did notice the TG thing is skinny ..more like a curtain rod than muffler sized. could that be backing stuff up?
Yes, back pressure is a contributing factor. Besides being skinny, the cut away shows that there is another inner pipe, so even less space for the exhaust gasses to go. If it becomes to restrictive then the motor will stop running.
And I will work on a ELI5 post later this evening.
EDIT: picture didn't work, fixed now.